1. Field of the Invention
The present invention relates to a threshold computation apparatus and a threshold computation program.
Priority is claimed on Japanese Patent Application No. 2011-038202, filed Feb. 24, 2011, the contents of which are incorporated herein by reference.
2. Description of the Related Art
In a radio communication system based on LTE (long term evolution) which is one of communication standards, a user terminal receives a pilot signal of a downlink from a base station, and sends the base station measurement information which is called “MR” (Measurement Report) and indicates received power or communication quality of the pilot signal. Based on a result of comparison between the measurement information and a predetermined threshold, the user terminal determines whether or not the measurement information will be sent to the base station (see Non-Patent Documents 1, 2, and 3).    Non-Patent Document 1: 3GPP TS 36.214 v9.2.0 2010-06    Non-Patent Document 2: 3GPP TS 36.331 v9.3.0 2010-06 (see pp. 72-78)    Non-Patent Document 3: 3GPP TS 36.304 v9.3.0 2010-06
The predetermined threshold used in the above determination is computed by the base station, and sent from the base station to the user terminal. The base station computes the threshold based on the measurement information received from the user terminal in advance, or on a value which is predetermined.
The reason for computing the threshold based on the pilot signal for the downlink is that the pilot signal for the downlink is sent by broadcasting from the base station. That is, even a user terminal, which has not been able to be synchronized with the base station in an uplink, can receive a pilot signal for a downlink, and thus the pilot signal for the downlink is convenient for computing received power and communication quality with respect to the relevant user terminal.
Accordingly, the threshold used in the determination by the user terminal whether or not the measurement information will be sent to the base station is computed based on a pilot signal for a downlink.
However, the threshold computed based on a pilot signal for a downlink may not have an appropriate value due to interference power from terminals which access a neighbor base station. If the threshold does not have an appropriate value, measurement information which should be sent is not sent from the user terminal to the base station, or measurement information which should not be sent is sent from the user terminal to the base station. In this case, a process performed based on the measurement information is also not appropriately executed, which may causes an interruption of communication.